Trap seal primer valves are used for charging water into sewer line water traps to prevent the escape of sewer gases. Under normal conditions, the level of water in sewer line traps decreases through evaporation by about one-eighth of an inch for each twenty-four hour period. Accordingly, most municipal plumbing and sanitary codes require that means be provided for supplying water to the traps automatically or periodically to assure that the trap water level will be sufficiently high to render the trap operative and functional at all times.
To supply water to the traps automatically, it is usual to connect the trap to the house water line through a priming valve that is actuated by variations in pressure in the house line and acts to charge the trap with water upon each fluctuation of pressure in the house line. These primer valves are required to operate over long periods of time with minimum maintenance.
Many difficulties are associated with the use of conventional trap seal primers. Some of the primers require adjustment to the line pressure in order to function. Others require awkward adjustment to provide the desired metered amount of water. Also, some of the prior art units have an internal screen filter to contain calcium, iron, and other deposits that occur in municipal water supplies. When these filters become clogged, flow is constrained and disassembly of the trap seal primer may render it inoperable. Finally, moving parts in primers are subject to corrosion and failure, especially where springs are involved.
What is needed is a trap seal primer valve for sewer trap lines that does not require any special adjustment for line pressure or amount of water delivery, that dispenses a predictable amount of water in response to a minimal pressure drop (e.g., 3 lb.) occurring in the supply line, that will not flow continuously while the line is returning to normal pressure, that prevents backflow from the trap to the water line, that is simpler in construction and that has an easily replaceable mesh filter and cartridge.